This invention relates to polyvinyl alcohol soft contact lenses and their use, which have been annealed under substantially ambient conditions in the presence of an annealing promoter solvent. This invention further relates to a process for producing annealed shaped polyvinyl alcohol hydrogels useful for contact lenses.
Polyvinyl alcohol films and gels have been reported as ophthalmic inserts, e.g. in the lower conjunctival sac when imbibed with pharmaceuticals such as tetracycline, pilocarpine, atropine and the like. Such materials are generally in the form of a crosslinked film or gel. See, for example, Y. F. Maichuk, Ophthalmic Drug Inserts, Invest. Ophthalmol., Vol. 14, pages 87-90 (1975); D. W. Lamberts, Solid Delivery Devices, Int. Ophthalmol. Clininc, Vol. 20, No. 3, pages 68-69 (1980); and Y. E. Maichuk, Antibiotik, Vol. 12, No. 4, pages 432-5 (1967). In U.S. Pat. No. 3,408,423, polyvinyl alcohol crosslinked with glyoxal has been proposed as a hydrogel contact lens material. In U.S. Pat. No. 4,559,186, hydrogel contact lens materials crosslinked with a borate is described. In U.S. Pat. No. 4,619,793, polyvinyl alcohol is annealed to increase the crystallinity thereof and swollen in a swelling solvent. Such annealing is conducted, inter alia, by evaporation of an aqueous or aqueous/plasticizer polyvinyl alcohol gel, by high pressure stress induced crystallization of solid state polyvinyl alcohol, or by thermally annealing optionally plasticized polyvinyl alcohol at elevated temperatures, in each case to form a polyvinyl alcohol at elevated temperatures, in each case to form a polyvinyl alcohol lens replica and then swelling the replica in a swelling solvent, such as water, to form the swollen hydrogel lens. Because the final lenses are swollen, the configuration of the annealed lens replica, for example, must be calculated based upon the predicted extent of swelling which occurs subsequent to the lens replica step. In U.S. Pat. No. 4,874,562, there is exemplified a method of crystallizing a polyvinyl alcohol aqueous/organic solvent solution by cooling the solution to 0.degree. C. or less, preferably about -20.degree. C., to crystallize out the polyvinyl alcohol and immersing the resulting gel in water. However, such gels generally undergo a size change of about 15 to about 30 percent when solvents are exchanged with water or a saline solution.
It is an object of the present invention to provide contact lenses of polyvinyl alcohol gels which can be economically prepared in molds which substantially conform to contact lens dimensions when worn by the patient.
It is further object of the present invention to provide processes for the preparation of such lenses.
It is further object of the present invention to provide a method of correcting vision in patients in need of the same by wearing such a lens on the surface of the cornea.